(19)
(11) EP 0 936 019 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
21.03.2001 Bulletin 2001/12

(43) Date of publication A2:
18.08.1999 Bulletin 1999/33

(21) Application number: 99301027.1

(22) Date of filing: 12.02.1999
(51) International Patent Classification (IPC)7B23K 9/10, B23K 9/073
(84) Designated Contracting States:
AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE
Designated Extension States:
AL LT LV MK RO SI

(30) Priority: 17.02.1998 US 24944

(71) Applicant: ILLINOIS TOOL WORKS INC.
Glenview, Illinois 60025 (US)

(72) Inventors:
  • Hutchison, Richard
    New London, Wisconsin 54961 (US)
  • Uecker, James
    Appleton, Wisconsin 54911 (US)
  • Holverson, Todd
    Appleton, Wisconsin 54914 (US)

(74) Representative: Rackham, Stephen Neil 
GILL JENNINGS & EVERY, Broadgate House, 7 Eldon Street
London EC2M 7LH
London EC2M 7LH (GB)

   


(54) Method and apparatus for welding


(57) A short circuit arc welding system has a control scheme uses a current command signal to drive the output current. The command signal is comprised of a long-term current command that sets the long-term current command level and a real time or short-by-short current command. Arc voltage feedback is led to determine if the desired arc length is present and to adjust the long-term command. The short-by-short current command , derived from real-time arc current feedback and is used to control the burn-off rate by an instantaneous, or short-by-short, adjustment of the current command. A function of the time derivative of arc power, less the time derivative of arc current, is used to detect, in real time, when the short is about to clear. A stop algorithm is employed that monitors the arc on a short-by-short basis. When the process is ending a very low current level is provided to avoid forming a ball. However, if a short is created, Qreq after the low current level, a burst of energy is provided to clear or burn off the short. After the short is cleared, very low current is again provided to avoid forming a large ball. This is repeated until the wire stops and the process ends.





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